1. Field of the Invention
The present invention relates to a rotor for a rotary electric machine and in particular to a rotor that includes a rotor core in which a magnet is provided.
2. Description of Related Art
It is being in practice that a magnet-embedded rotor of a rotary electric machine is cooled by using a coolant such as a cooling oil.
For example, Japanese Patent Application Publication No. 2008-228522 (JP 2008-228522 A) discloses a rotor of a rotary electric machine that is formed with a coolant flow path extending through a magnet-provided rotor core from its inner periphery to outer periphery, the core being formed by combining or laminating steel plates each of which is formed with a slit.
In addition, Japanese Patent Application Publication No. 2006-67777 (JP 2006-67777 A) discloses a cooling structure of a rotary electric machine that is formed with a coolant flow path extending through a rotor core from its inner periphery to outer periphery, the core being formed by laminating steel plates each of which is formed with a slit that extends outward in a radial direction form a shaft hole formed at a central portion of the core to an outer circumferential portion.
Furthermore, Japanese Patent Application Publication No. 2008-312343 (JP 2008-312343 A) discloses a motor device with a magnet cooling structure in which a coolant received from a shaft at an axially central portion of a rotor core is guided toward magnets and then is caused to flow to opposite ends of the rotor core in order to cool the magnets in the rotor core.
Still more, Japanese Patent Application Publication No. 2010-263757 (JP 2010-263757 A) discloses a coolant flow path in a cage-type induction machine, though this is not intended to cool magnets provided in a rotor core, which extends through the rotor core from its inner periphery to outer periphery, the core being formed by combining or laminating steel plates each of which is formed with a slit.
Magnets, which are provided in a rotor core to extend along an axial direction of the rotor core, are apt to have a high temperature due to a heat accumulation at an axially central portion of the rotor core. Thus, for suppressing the generation of, irreversible thermal demagnetization caused by high temperature, it is desirable to cool an axially central portion of each magnet with a high priority. For this purpose, in the rotor core that is formed by laminating electromagnetic steel plates in an axial direction, if a coolant flow path, which guides in the rotor core a coolant from the shaft toward the magnets, is formed by elongated slits in a radial direction, the centrifugal force during rotation of the rotor increases the resulting stress applied to the slit-formed portion of the electromagnetic steel plates, which may cause the strength of the electromagnetic steel plates to reduce.